An electrical machine, such as generators for wind turbines, may consist of a rotor and a stator. The stator may be composed of a stack of laminations, wherein one or more coils or windings may be arranged in recesses of the stator lamination stack.
In such electric machines, heat is generated when transferring mechanical energy in to electrical energy and vice versa. The heat is generated in both the copper conductors that form the windings of the stator by Joule losses and the iron parts of magnetically active components by eddy current losses. The generated heat has to be removed in order to avoid hotspots, power reduction due to increased magnet temperature and insulation wearing.
In common systems, the stator lamination stack and the attached windings are cooled by blowing air inside the stator. In axial end sections of the stator housings the windings protrude and form a half loop. The protruding half loops of the windings form the end windings of the stator windings. The stator windings are cooled by blowing air through the windings, for example in an air gap between rotor and stator or through radial extending ducts of the stator housing. The cooling of segments has been undertaken with an air to air heat exchanger that is mounted per segment. As the number of segments increases, the cooling requirements will increase and hence increasing the weight and complexity of the geometry of the stator and the cooling part. The mounting and the air piping will also pose problems for construction, and lifetime of the generator expected may not be fulfilled due to larger service requirement. In such systems, the stator laminations are welded to underlying T bars and fixed at the ends by pressure plates. The stator stack is provided with a number of axial spacers for cooling and hence hereby reducing stiffness of the segments after assembly.
An uneven flow of cooling air may occur in such cooling systems and may cause uneven machine performance regarding temperature and may further require larger fan powers to address hot spots especially in the end windings. In addition, axial cooling channels provided in the stator stack may reduce the structural integrity of the segments.
Thus, there may be a need for an improved system for dissipating heat from a stator lamination stack.